With a trend of intelligent vehicles and electric vehicles, the mechanical structure of traditional vehicles has changed. Independent steering mechanism for left and right wheels arises at the historic moment. The steering mechanism can be applied to vehicles of various structures, especially suitable for distributed drive electric vehicles. The distributed drive electric vehicles can be four-wheel driven independently, have more control degree of freedom, and the security, power performance and stability of the vehicles can be improved with a reasonable control algorithm. Therefore, this kind of vehicles has been widely studied. As for the realization of the structure of the distributed drive electric vehicle, each wheel is equipped with a wheel hub/wheel rim driving system, and the steering system may be a traditional steering mechanism or an independent steering mechanism, so that the motion of the vehicle can be better controlled by four-wheel independent steering and independent driving.
In a China Patent CN 205075885 U, a steering motor is vertically disposed above a wheel which can realize four-wheel independent driving and improve stress condition of the steering mechanism. However, there is no locking mechanism on the left wheel and right wheel. Therefore, once a certain steering motor malfunctions, the steering function can not be achieved. In CN205113422U, a switch between independent steering to integral steering is achieved by engagement of slots and teeth. However, a process of the engagement is not smooth and the response is slow, which will affect driving feelings. Moreover, due to lacking a mechanical connection between a self-locking mechanism and a steering wheel, the system is hard to maintain the direction under the interference of the outside world.
Independent steering for the left wheel and right wheel makes the control of the vehicles more flexible. Tire wearing can be reduced and driving stability of the vehicles can be improved by modifying steering angles of left wheel and right wheel separately. However, there are still some technical problems required to be solved. The steering motor has poor ability to withstand external interference, thus a transmission device with a special mechanical structure or of high reverse efficiency is needed. Under some specific conditions, the left steering wheel and the right steering wheel are required to be switched from an independent motion to an integral motion. Due to cancellation of the mechanical connection between the steering wheel and a steering tie rod, the steering system cannot work normally when a motor on one side is broken. Therefore, a redundant design is required for the steering system, so as to improve fault-tolerant capacity of the steering system.